Olivia Grace stopped by and gave us a great healing macro for Arenas that heals her or her party members by her modifier. Genius!

#showtooltip Greater Healing Wave
/cast [mod:alt,@party1] Greater Healing Wave
/cast [mod:shift,@party2] Greater Healing Wave
/cast [nomod] Greater Healing Wave

Macroexplain.com explains it like this:

If you were holding the alt key then:
Cast Greater Healing Wave on party member 1

If you were holding the shift key then:
Cast Greater Healing Wave on party member 2

If you were not holding any modifier key down then:
Cast Greater Healing Wave on the currently targeted unit